AVS 49th International Symposium
    Plasma Science Wednesday Sessions
       Session PS+MM-WeA

Paper PS+MM-WeA8
Profile Control as a Function of Process Parameters in Deep Anisotropic Etching of Silicon

Wednesday, November 6, 2002, 4:20 pm, Room C-105

Session: Feature Profile Evolution /Plasma Processing for MEMS
Presenter: M.L. Steen, IBM T.J. Watson Research Center
Authors: M.L. Steen, IBM T.J. Watson Research Center
T.J. Dalton, IBM T.J. Watson Research Center
Correspondent: Click to Email
Deep etching of silicon is integral to the fabrication of microcomponents for microelectromechanical systems (MEMs). New commercially-available etching tools from several manufacturers are capable of deep silicon etching beyond 300 µmm. These systems offer the time multiplexed deep etching (TMDE) technique developed and licensed by Robert Bosch Gmbh, which uses alternating etching and deposition cycles for anisotropic etching of deep silicon structures. During the deposition step, sidewalls are passivated by a polymer deposited from a C@sub@4F@sub@8 discharge. During the subsequent etching cycle flowing only SF@sub@6, both the polymer and silicon are preferentially etched from the base of the trench by ion bombardment. Accurate control of the depth and anisotropy of etched structures is achieved by a fine balance between deposition and subsequent removal of the passivating layer. Processes are well controlled and many types of MEMS devices, such as pressure sensors and accelerometers, are produced using this technology. We are interested in expanding the number and scope of applications using deep silicon etching. Many of these applications have additional demands on surface morphology including minimization of the scalloping observed on vertical sidewalls during TMDE and the roughness of surfaces exposed to the discharge. Moreover, mask undercut and bowing of the etch profiles must be reduced to tailor the slope of etch profiles. Our goal is to understand the evolution of these traits as a function of operating conditions. Toward this goal, a number of process variables were explored using a commercial inductively-coupled plasma etcher. We report a significant increase in the silicon etching rate, minimization of mask undercut, and substantial reduction in bowing. These improvements demonstrate enhanced process performance and flexibility to meet a broad range of needs in deep silicon etching.